The pair face each other at Molineux on Sunday with Doherty backing the clubs to have an impact at the top this season.

"I think the teams outside the top six are getting better. There is definitely more investment in those clubs as well as they have a lot more money to spend," said the defender, with Wolves fifth before the weekend.

"So the gap is getting smaller although they are still top teams and for the majority of the time they still finish in the top six but the rest are strong and definitely catching up."

Wolves are building on last season's seventh-placed finish which saw them qualify for the Europa League after Watford lost the FA Cup final to Manchester City.

They reached the last 32 with a 3-3 draw against Braga on Thursday, with Doherty scoring in Portugal, and he believes Sheffield United took note of their success.

"I guess they saw a blueprint and saw that it worked," said the Republic of Ireland international.

"But I guess they were playing that shape (three at the back) for a long while and they have a slightly different way of playing it to what we do.

"Fair play to them, they have done unbelievable so far and don't look out of place in the Premier League.

"I have friends there so I am happy for them but on Sunday it will be down to business and I'll be trying to beat them.

"There are a lot of players who have the ability and yet, for whatever reason, they never get the chance.

"I guess guys like me and Coads (Conor Coady) got our chance because we were part of promotion winning teams."

Doherty also faced the Blades when Wolves were in Sky Bet League One six years ago after tumbling down from the Premier League.

He added: "Yeah, we met them in League One and in the Championship a couple of seasons ago – now we're coming up against each other in the Premier League.

"It just goes to show the form they've shown over the last couple of years. Their club is on the up just like ourselves."